1. Field of the Invention
The present invention relates to a method for producing a magnetic head for detecting intensity of an external magnetic field by detecting the value of resistance of a magnetoresistive element, wherein the resistance changes dependently on the intensity of the external magnetic field.
2. Description of the Related Art
In recent years, a great deal of information has been routinely handled as the use of computers spreads. In order to record or reproduce such a great deal of information, hard disk drives (HDDs) are used, which are characterized by having a large memory capacity and a high speed for accessing information. In general, HDDs have a magnetic disk whose surface is composed of a magnetic material, and a composite type magnetic head wherein a recording head for recording information on the magnetic disk and a reproducing head for reproducing the information recorded on the magnetic disk. The recording head has a minute coil, and is arranged close to the magnetic disk. Respective microscopic areas (1-bit areas) in the surface of the magnetic disk are magnetized by a magnetic field generated from the coil of the recording head, so that information is recorded on the magnetic disk. The reproducing head outputs an electrical reproducing signal corresponding to the magnetic field generated by magnetization from each of the 1-bit areas. The information recorded on the magnetic disk is reproduced through the reproducing head.
At present, in many reproducing heads mounted on HDDs, a magnetoresistive head (MR head) is used, wherein magnetoresistance effect that resistance changes dependently on an external magnetic field is used. With improvement of recording density of magnetic disks, spin valve magnetoresistive heads (referred to as “SVMR heads” hereinafter) are being earnestly made practicable. The SVMR heads have particularly high sensitivity among MR heads, that is, generate change in output dependently on change in an external magnetic field.
The SVMR head has a spin valve element composed of a multilayer film comprising a free magnetic layer wherein the direction of magnetization changes dependently on an external magnetic field, a nonmagnetic metal layer, a fixed magnetic layer wherein the direction of magnetization is fixed, an antiferromagnetic layer which generates an exchange coupling magnetic field for fixing the magnetization direction of the fixed magnetic layer; and a shield layer for shielding this spin valve element magnetically. The spin valve element generates change in its resistance dependently on relative change in the angle between the direction of magnetization in the fixed magnetic layer and the direction of magnetization in the free magnetic layer. High sensitivity of the SVMR head originates from the fact that this resistance change is great.
In the spin valve element, hard magnetism layers are arranged, which apply a bias magnetic field to the free magnetic layer so that the free magnetic layer is divided by single-domains. Electrode terminals are also arranged, which send sense current Is to the spin valve element when the SVMR head is operated. When this SVMR head is made close to the magnetic disk and the two are relatively moved in the state that the sense current Is is sent, the value of the electrical resistance of the spin valve element successively changes dependently on signal magnetic field Hsig from the magnetic disk. An output voltage having a value represented by the product of the value of the electrical resistance and the sense current Is is outputted. A waveform representing change in the output voltage with the passage of time is referred to as a “reproduction waveform” hereinafter.
The spin valve element is preferably a spin valve element whose electrical resistance linearly changes dependently on the change in the signal magnetic field Hsig from the magnetic disk. In order to realize such linear change, the angle between the directions of magnetization in the fixed magnetic layer and the free magnetic layer is ideally 90° in the state that the signal magnetic field Hsig is not present. This angle is adjusted, for example, by subjecting the spin valve element of the SVMR head, when being made, to a pin annealing treatment in which the spin valve element is heated while a magnetic field is applied in a given direction for fixing magnetization of the fixed magnetic layer; and then conducting a free return treatment in which application of a magnetic field and heating are simultaneously performed so that the directions of easy axes of magnetization in the free magnetic layer and the shield layer are made perpendicular to the fixed magnetization direction in the fixed magnetic layer.
Production of a magnetic head requires various heat treatments, such as heat treatment for hardening a resist which surrounds the coil in the recording head. Even if these heat treatments are conducted in the state that no external magnetic field is applied, for example, the fixed magnetic layer receives the antimagnetic field of the fixed magnetic layer itself so that the magnetization of the fixed magnetic layer is inclined. As a result, the above-mentioned angle is off from the above-mentioned perpendicularity. By this angle gap, the following trouble arises: in the SVMR head, its output voltage does not respond linearly to the input of the signal magnetic field Hsig, so that the reproduction waveform is distorted.